1. Field of Invention
The present invention relates to means operable to: (i) be interposed between the power line and the power input terminals of a load means, and (ii) control the frequency, magnitude and/or waveshape of the voltage provided to the power input terminals of the load means.
2. Elements of Prior Art
One way of controlling the RMS magnitude and the waveshape of the voltage provided to a load from a power line is represented by a so-called light dimmer; which light dimmer is based on the phase-control of a Triac. However, this type of magnitude and waveshape control has only limited applications; and is, for instance, not useful in connection with loads having a substantial inductive component, such as a fluorescent lighting fixture or an electric motor. Of course, a Triac-type light dimmer is not capable of providing for frequency control; nor is it capable of providing control of waveshape independent of the waveshape of the voltage on the power line.
Other, more flexible methods for controlling the magnitude and waveshape of the voltage provided to a load from an ordinary power line have been described; and some of these methods are indeed usable with inductive loads. One such method is described in U.S. Pat. No. 4,350,935 to Spira et al. However, in the arrangement of Spira et al., there is no provision for frequency control.